A language \(L\)  is semilinear if \(\psi (L)\)  is a semilinear set. Equivalently, a language is semilinear if and only if it is letter-equivalent to some regular language [1]}. A family of languages is semilinear if all languages in it are semilinear, and it is said to be effectively semilinear if there is an algorithm to construct the constant and periods for each linear set from a representation of each language in the family.
For example, it is well-known that all context-free languages are effectively semilinear [2]}.
